1. Technical Field
The present invention relates to an improved method for the production of potato chips and more particularly to a method for continuously making kettle style potato chips which are similar in taste and texture to those kettle style potato chips produced by a traditional batch process.
2. Description of Related Art
Commercial production of potato chips typically involves a continuous process wherein sliced potatoes are continuously introduced into a vat of frying oil at a temperature of about 365° F. (about 185° C.) or higher, conveyed through the oil by paddles or other means, and removed from the oil after about two and one-half to three minutes of frying by an endless conveyor belt when the moisture content of the chips has been reduced to about 2% by weight or less. The resulting product generally has texture and flavor characteristics which are usually recognizable by consumers as typical commercially produced continuous process potato chips.
Potato chips produced by batch processes in kettle fryers have texture and flavor characteristics which are usually recognized by consumers as being distinctly different from typical commercially produced continuous process potato chips. As the name implies, batch process kettle frying of potato chips involves placing a batch of potato slices in a kettle of hot oil, e.g., at a temperature of about 300° F. (about 150° C.). In the conventional kettle fryers used in the production of kettle-style chips, the cooking oil temperature follows a generally U-shaped time vs. temperature profile as illustrated in FIG. 5 of U.S. Pat. No. 5,643,626, assigned to the same assignee as the present invention, which is hereby incorporated by reference. Upon introduction of the potato slices into the oil, the temperature of the oil typically drops quite rapidly by as much as 50° F. (about 28° C.) or more. As depicted by the Figure, the oil temperature falls to a low point temperature of about 235° F. to about 240° F. for a low point time of about 4 minutes. Heat to the kettle is then quickly increased and then the temperature of the oil begins to gradually rise, reaching about the initial frying temperature of about 300° F. The resultant potato chip has a moisture content of between 1.5% to 1.8% by weight.
Batch fried chips are generally harder and more crunchy than continuously fried chips and have a flavor that some consumers find more appealing than typical continuously fried commercial chips. It is believed in the art that the U-shaped temperature-time profile imparts the intense flavor and unique mouth feel characteristic of kettle-style chips. The commercially available kettle fryers, however, are relatively unsophisticated equipment that are significantly constrained by burner capacity and heat transfer capacity. Thus, the observed U-shaped temperature-time profile is unavoidable with the conventional kettle equipment, as the system cannot supply heat quickly enough to overcome the large heat sink created by the addition of a batch of raw potato slices. Changes in oil volume, initial fry temperature or potato batch weight will cause changes in temperature profile and finished product attributes. Therefore, the production of potato chips having the desired kettle-style attributes requires the adjustment of the process parameters in a manner that results in the U-shaped temperature-time profile.
Production rates using batch kettle fryers are dependent upon the equipment used. The modern kettles that are utilized in batch processes are generally manufactured of stainless steel, and vary in size and capacity. The kettles typically are heated by gas burners positioned directly under the kettle floor. Fryer capacities range from as few as 60 pounds per hour to up to 500 pounds per hour (finished product basis), although most batch fry operations have kettle fryers that can manufacture between 125 and 200 pounds of chips per hour. In order to efficiently use a batch kettle fryer of a given size, it is necessary to maintain a particular “load” or amount of potato slices per volume of oil, in order to produce the desired U-shaped temperature-time profile. These and other constraints provide limits on the amount of throughput using batch kettle fryers. By contrast, potato chips made by a continuous process can employ continuous fryers capable of producing 1,000 to 5,000 pounds per hour of finished product. The kettle or batch process is therefore less economical than a continuous process.
Consequently, there is a need in the art for an efficient continuous process for the production of potato chips having batch-fried texture and flavor characteristics. Specifically, there is a need for increasing the production rate and production efficiency of fried kettle-style potato chips without diminishing the desired hard bite texture and flavor.
Several attempts have been made in the prior art at solving this problem. Such attempts are illustrated by U.S. Pat. Nos. 4,741,912, 4,929,461, 4,863,750, and 4,956,189. However, these solutions all fail to produce a continuous process having a U-shaped temperature-time profile.
Another prior art solution to this problem is illustrated by U.S. Pat. No. 4,923,705, assigned to Borden, which discloses a continuous method for making kettle style potato chips. FIG. 1 is a schematic representation of the invention disclosed in the Borden patent. The drawing shows various features of the apparatus including, a slicer 1; an oil flume 3 outfitted with agitating means 5 having an adjustable flap 10 situated at the flume outlet; an elongated fryer vessel 4 having a plurality of oil entry ports and equipped with longitudinal paddle assemblies 15; a submerging conveyor 17; an optional oil spray 18; a take-out conveyor 19; an oil pump 20; and a heat exchanger 21 for heating oil external to the apparatus.
The apparatus has a first oil inlet port 2 situated at the infeed end of the flume; the second oil inlet port 7 near the entrance end of the fryer; and the third oil inlet port 11 two-thirds of the way down the length of the fryer. Also disclosed is a fourth oil inlet port 9, situated between the second and third oil inlet ports. The purpose of these multiple oil inlet ports is to provide a specific temperature profile throughout the fryer. Unfortunately, this configuration fails to produce a desirable temperature profile or an easily controlled temperature profile. Like many of the prior art solutions, this configuration uses product load to drop the oil temperature and then adds hot oil to the fryer to increase the temperature. Thus, it is especially difficult to mimic the trough section of the U-shaped temperature-time profile. For example, the Borden patent teaches admitting oil by way of the second oil inlet 7 with either re-heated oil (having a temperature of 300° F. to about 320° F.), non-reheated oil (having a temperature of 285° F. to about 300° F.), or mixtures of re-heated and non-reheated oil. Thus, the temperature of oil entering the second oil inlet 7 at the beginning of the second zone necessarily ranges from 285° F. to 320° F. Further, oil from the flume is entering the second zone at a temperature of about 250° F. to about 275° F.
Given these oil inlet temperatures, one can see the difficulty in achieving an oil temperature in the second zone of about 240° F. to about 265° F. as called for by the Borden patent. This process is very dependent upon product load to achieve the desired low temperature drop for the desired time. In addition, the entire volume of oil from the flume and the second inlet 7 must then be heated in the third zone to a temperature of between about 285° F. and 310° F., a difficult scenario given the available driving force. For example, the heating means for heating the large amount of oil in the fryer is limited to hot oil having a temperature of only 300° F. to about 320° F., just a few degrees above the third zone target temperature. Thus, the disclosed configuration fails to provide an easily controllable temperature profile within a continuous fryer.
Similarly, U.S. Pat. No. 5,137,740, assigned to Heat and Control, discloses a multi-temperature zone fryer that mixes hot oil at a temperature of 300° F. to about 310° F. with the fryer oil to change the rate of temperature drop within a second zone. Again, attempting to mimic the trough section of the U-shape temperature-time profile with the use of product load and injected hot oil at over 300° F. has proven difficult.
Consequently, a need exists for improvements in the continuous production of kettle-fried potato chips. The improved method should mimic the temperature-time profile of a potato chip made from the traditional batch process. Further, the improved method should provide a way to better control the low point temperature for the desired amount of time. Moreover, the improved method should provide a way to better control the temperature rise that occurs subsequent to achieving the desired low point temperature for the desired amount of time.